In the field of cardiology, radioactive probes can provide information on the physiology and pathophysiology of the heart function, e.g. by myocardial perfusion, metabolism or innervation. Two 99mTc radiopharmaceuticals, Sestamibi and Tetrafosmin, are commercially available and approved for myocardial perfusion studies. These radiopharmaceuticals, which consist respectively of lipophilic Tc(I) and Tc(V) cationic complexes, suffer from low heart/liver and heart/lung uptake ratios, and so are not entirely satisfactory for myocardial perfusion studies. We have therefore been seeking alternative and better performing 99mTc complexes for myocardial imaging, profiting from the recently-introduced so-called organometallic labelling approach. This approach is based on complexes containing the fac-[99mTc(CO)3]+ core and is assuming a growing importance in the development of 99mTc radioactive drugs for diagnostic medical applications.
We have now found that the combination of this organometallic core with appropriate ligands (appropriate in terms of charge, denticity or topology) provides cationic and lipophilic 99mTc complexes with the biological properties required for myocardial imaging.